There are many different arc welding processes used for numerous welding applications. While different processes have characteristics that render them desirable for particular applications, different processes share some characteristics, such a tendency to cause spatter when the arc is formed, such as at the beginning of a weld (particularly for a touch start) or when transitioning from a short circuit to an arc during the weld.
Spatter is caused during starts because the wire bridges to the work piece, forming a short, and resistive heating melts or softens wire and creates an arc in the middle of the wire bridge. The process causes spatter of the wire from the location where the arc formed to the wire on the workpiece. The wire continues to feed, and the process is repeated until a stable arc forms.
Prior art attempts at reducing spatter from starts include the Jetline® retract start. This provides for retracting the wire. The wire retraction causes an arc to form between the end of the wire and the workpiece, and reduces the likelihood of resistive heating with an arc forming midway between the gun and the workpiece. Other welding power supplies also provide a retract start.
Spatter is caused during the welding process when transitioning from the short circuit state to the arc state primarily by the high current needed to “pinch” off a droplet. The pinching off at high current can result in a violent disintegration of the molten metal bridge producing excessive weld spatter. Instability also results from the weld pool being pushed away.
Many attempts in the prior art were made to create a stable short circuit welding power supply, such as those shown in U.S. Pat. Nos. 4,717,807, 4,835,360, 4,866,247, 4,897,523, 4,954,691, 4,972,064, 5,001,326, 5,003,154, 5,148,001, 5,742,029, 5,961,863, 6,051,810 and 6,160,241. These patents generally disclose complicated control schemes that fail to control the process to provide a stable and effective weld. They include control schemes that try to control the deposition of material and/or predict or cause a transition to the subsequent state based on the total energy put into the weld, the length of the stick out, total watts, time of the preceding state, etc.
CSC (controlled short circuit) welding provides for retracting or slowing the wire during the transition from short to arc, and is described in U.S. Pat. Nos. 7,364,059, 7,351,933, 7,165,707, 7,138,602, 7,102,099, 6,969,823 and 6,963,048 (each of which is hereby incorporated by reference). Spatter is reduced by controlling the transition with the retraction (or slowing) of the wire, and by controlling the energy put into the weld with the current-voltage waveform. While these systems reduce spatter, they are particularly suited for processes with short circuits.
There is a need for a spatter control for low cost manual welding applications, and/or open arc welding processes.